Known convertiplanes substantially comprise a fuselage, a pair of semi-wings projecting on opposite lateral sides of the fuselage, and a pair of nacelles which house relative rotors and rotate, together with relative rotors, relative to respective semi-wings.
Each nacelle houses a relative motor-rotor assembly, which, therefore, rotates together with the nacelle relative to the corresponding semi-wing.
In detail, each nacelle comprises:                a gas turbine; and        a mechanical transmission which mechanically connects the gas turbine with the relative rotor.        
Each mechanical transmission is adapted to convert the higher rotation speed of the gas turbine into the lower rotation speed need for an efficient operation of the rotors.
To this purpose, the mechanical transmission comprises a plurality of gearbox, shafts and bearing.
As a result, the mechanical transmission increases the weight, the complexity and the maintenance requirements of the convertiplane.
In order to reduce all the above-indicated drawbacks which are connected with the presence of the mechanical transmission, WO-A-2009/079049 discloses a helicopter comprising:                a main rotor;        a first electric motor for driving in rotation the main rotor;        a tail rotor; and        a second electric motor for driving the tail-rotor.        
Electric motor are supplied by an on-board power source, such as a battery, an hybrid source of electricity or the like.
However, the on-board power source needs to be periodically re-charged.
In the recent years, the attention has been focused on environmental issues of air pollution and climate change.
As a consequence, a need is felt within the industry to re-charge the on-board power source by using renewable energy, in particular wind energy. Unfortunately, the wind energy is particularly difficult to collect because the orientation of wind current is variable.
Known convertiplanes also comprise mechanical brakes for slowing down and stopping the angular speed of rotors. However, mechanical brakes are heavy and comprise hydraulic system which are costly to maintain. Moreover, mechanical brakes dissipate as waste heat a large amount of energy.
A need is felt within the industry to brake the rotors without requiring costly and complex components and/or while reducing the amount of kinetic energy wasted as heat.
Furthermore, a need is felt to contain as far as possible the size and the weight of the nacelles.
A need is also felt to manufacture a modular convertiplane which may be easily fitted with different propulsion packages.
Known convertiplanes make also wide use of hydraulic actuating system, for example for tilting rotors and/or for actuating landing gear and/or for controlling the blades of the rotor. Hydraulic actuating systems require an oil tank on the convertiplane, are costly to maintain, generate a certain risk of fire and require that oil is disposed in the environment.
A need is felt to manufacture a convertiplane, which, as much as possible, overcome the drawbacks connected with the use of hydraulic actuating systems.